Sidenote;
In their GPO enabled version you can only force settings, not set them as defaults. There also have been issues with default browser settings in the earlier MSIs. Not sure if this is still a problem, i made my own solution to the issue.

Follow this for creating MSI. It works for version 9, 10 and 11.
http://msiworld.blogspot.com.au/2012/01/packaging-mozilla-firefox-901.html
Follow my blog for more updates and other useful information.